Aqueous and ethanolic extracts of Piliostigma reticulatum, a herb widely
used for the treatment of diarrhea in southwest Nigeria, was challenged with
clinical isolates of Escherichia coli,
Shigella dysenteriae, Salmonella typhimurium, Staphylococcus aureus and Pseudomonas
aeruginosa. The ethanol extract exhibited the highest activity against
the test organisms with zones of inhibition ranging from 16.0 � 20.0 mm,
followed by the hot aqueous extract and the cold aqueous extracts, with zones
of inhibition ranging between 8.0 � 10.0 mm and 4.0 � 7.0 mm respectively.
The Minimum Inhibitory Concentration (MIC) ranged between 0.025 � 0.25% w/v
and photochemical analysis showed that the plant possesses saponins, tanins,
phenolics, phlobatinins and glycosides. A comparative analysis of the extract
with some conventional antibiotics namely; Chloramphenicol, Ampicillin and
Tetracycline showed that there was significant difference in the
antibacterial activity of the bark extract and the antibiotic standard
(P<0.05).

Herbal
medicine has been shown to be effective and about 60% of rural populations depend
on it for their primary health care (WHO, 1988; Akinyemi et al., 2000). This could be attributed to affordability,
accessibility, in the economic sense and socially, an uneven distribution of
health personnel between rural and urban areas. Traditional medical
practitioners in Nigeria use a variety of herbal preparations to treat
different kinds of ailments such as typhoid and paratyphoid fevers,
dysentery, malaria, diarrhea, etc. Various research works conducted in recent
years have shown that pathogenic microorganisms are becoming increasingly
resistant to existing antibiotics at alarming rates (Rotimi and Mosadimi,
1984; Spencer et al., 1986; Olayemi
and Oyagade, 1987; Monetiore et al.,
1993, Olukoya et al., 1993). Such high
wave of antibiotic resistance among pathogenic microorganisms creates
problems in health care delivery in relation to microbial infections in man
and animals.

Piliostigma reticulatum (DL.) Hochst. (common name;
Yoruba: �abafin�, Hausa: �kalgo�, Igbo: okpo atu�) belongs to the family
Leguminosae - Caesalpiniaceae and is found in the savannah region of Nigeria.
It is a tree, occurring up to 30ft in height with an evergreen, dense
spreading crown (Keay, 1989).

In recent past, attention has been
directed towards medicinal research to substantiate the claims of cure made
by traditional healers and thus provide scientific basis for their efficacy.
Several important drugs have been discovered in plants and are now
synthesized chemically for commercial purposes. However, the search for new
ones continues especially in the tropical plants. Akinsinde and Olukoya,
(1995) demonstrated activity of Terminaliaavicennoides against Vibrio cholerae and Salmonella typhi, Omojasola and Awe
(2004) reported the antimicrobial activity of the leaf extract of Anacardium occidentale and Gossypium hirsutum against Escherichia coli, Shigella dysenteriae,
Salmonella typhimurium,
Staphylococcus aureus and Pseudomonas
aeruginosa.

In
Nigeria, the research for new drugs is on course hence the need to
investigate the pharmacological potentials of Piliostgma reticulatum used traditionally in the treatment of
diarrhea.

Materials and Methods

Sample Collection

Sun
dried bark of the plant was purchased from the trado-medical section of the
Ilorin market. It was identified and authenticated at the Department of Plant
Biology, University of Ilorin.

Extraction

Cold
aqueous, hot aqueous and ethanolic extractions of the plant materials were
prepared as described by Oyagade et al.
(1999). A preliminary test had shown that the aqueous extract showed
greater activity at 800C than 280C. So the aqueous
extraction was done at 800C in water bath for 1� hours. The
extracts were decanted and filtered through Whatman No. 1 filter paper. The filtered
extract was sterilized using 0.45�m pore size membrane filter and evaporated
to dryness at 450C. The residues obtained were reconstituted in
95% ethanol as stock concentration of 250mg/ml.

Test Organisms

Clinical
isolates of Escherichia coil, Shigella
dysenteriae, Salmonella typhimurium, Staphylococcus aureus and Pseudomonas aeruginosa were collected
from the University of Ilorin Teaching Hospital, Ilorin, Nigeria. All inocula
were standardized using the method described by Bauer et al. (1966).

Antibacterial assay

The well
method of the agar dilution was used to determine the antibacterial activity
of the plant extracts and the antibiotics. The bacterial cultures were
inoculated on Mueller Hinton Agar (MHA) and were incubated at 37OC
for 24 hours. The MIC for the plant extracts was determined using the method
of Mann et al., 1997 and Oyagade et al., 1999).

Phytochemical screening of ethanolic extracts

The
extract was subjected to phytochemical screening for the presence of
alkaloids, tannins, phenolics, saponins, steroids, triterpenes, phlobatinin
and cardiac glycosides using the method described by Odebiyi and Sofowora,
(1978).

Results and Discussion

The
antibacterial activity of the cold aqueous, hot aqueous and ethanolic
extracts of P. reticulatum show
that the ethanolic extract exhibited greater activity than both the hot and
cold aqueous extracts (Table 1). The higher activity of the ethanolic
extracts may not be unconnected with the extraction solvent because ethanol
has been shown to be better solvent than water (Akinyemi et al., 2000). This may also account for the reason why the
herbal physicians prefer to use local alcoholic decoctions in extracting the
herbs rather than aqueous extracts in treating their patients. The ethanolic
extract was strongly positive for the presence of alkaloids, tannins and
phenolics and positive for the presence of triterpenes and phlobatinins
(Table 2). The presence of these phytochemicals is indicative of
antibacterial activity (Odebiyi and Sofowora, 1978).

The potential
of any drug is the active principle contained therein; many of these
secondary metabolites have prominent effect on animal systems and microbial
cells (Jung et al., 1990; Triguna et al., 1992 and Fatoba et al., 2003). The presence of these
metabolites therefore confers pharmacological potentials on this plant. Other
workers have also reported bioinsecticidal and antitrypanocidal properties of
P. reticulatum extract (Atawodi et al., 2003, Abdullahi and Muhammed,
2004).

The cold
water extract had least inhibitory effect on all the organisms used. The MIC
ranged from 0.025 � 0.25 %w/v with P.
aeruginosa having the highest value of 0.25%w/v (Figure .1). In the
comparison of the antibacterial activity of P. reticulatum with some conventional antibiotics, the results
indicate that the conventional antibiotics (Chloramphenicol, Ampicillin and
Tetracycline) demonstrated greater activity than the plant extract at the
same concentration (Fig. 2). The results also show that these differences are
significant at 5% significance level. The fact that the plant extract is only
a crude extract may account for some of these differences in activity. Higher
levels of antibacterial activity are expected from a purified sample of P. reticulatum whose active principle
has been isolated. The comparison of the activity of the plant extract with
conventional antibiotics confirmed reports by other workers. Emeruwa (1982)
reported that conventional antibiotics are more active than plant extracts.
These results thus confirm the basis of traditional use of P. reticulatum in diarrhea treatment.
Further study needs to be carried out on the isolation of the bioactive
components of the tested plant and their effect in vivo.

References

Abdullahi,
Y.M. and Muhammed, S. (2004). Assessment of the toxic potentials of some
plants powders on survival and development of Callosobuchus maculatus. African Journal of Biotechnology 3(1):60
� 62.